The compact disc, launched by Sony and Philips 19 years ago, was the first mass-market digital-music format, and for MP3 traders today, CDs are the original source of almost all studio-quality audio on the Internet.

But at the time of its introduction, the CD almost became another audiophiles' also-ran.

Compact discs were introduced at the Salzburg Easter Festival in 1981. Famed conductor Herbert von Karajan unveiled the format at an April 15 press conference.

The conductor's support and Sony's choice of venue were meant to convey an endorsement of the CD by the top echelon of the classical-music community. Von Karajan's 1962 recordings with the Berlin Philharmonic Orchestra of Beethoven's nine symphonies, released by Deutsche Grammofon in 1963, were some of the first stereo recordings of the vinyl-LP era.

Because of von Karajan's involvement and the initial emphasis on classical music, some observers dismissed the shiny discs as just another audiophile toy. U.S. record companies with no ties to Philips or Sony did not exactly trip over themselves to support the new format.

Had it not been for Sony's eventual acquisition of the U.S. label Columbia, the skeptics might have been right. It was Sony/CBS's release of pop and rock bestsellers from Pink Floyd, Billy Joel and Michael Jackson  including Jackson's Thriller with the hit "Billie Jean" (RealAudio excerpt)  in 1982 and '83 that initially widened the format's appeal from its original classical roots.

Sony engineers designed a prototype CD almost 12 inches wide that also held video. Philips developed a 4.5-inch disc that held an hour's worth of music and no video.

They compromised on a 74-minute capacity, 4.75-inch disc, but not, as was reported, to please von Karajan, who legend says demanded that the entire Ninth Symphony fit onto one disc. According to von Karajan archivist Sigrit Fleiss, the reference recording of Beethoven's Ninth is only 67 minutes long  leaving seven minutes to spare.

Sony introduced the first CD players in Japan in October 1982, Europe in March 1983 and North America in September 1983.

In the past, the physical contact of a stylus on a vinyl record eventually wore down the record, creating hisses and pops. Because the music on CDs is read by a laser beam, sound quality does not degrade.

Songs on CDs are quite large as computer files. But because they are just a series of ones and zeroes, they can be compressed with mathematical formulas. By 1997, the compression format known as MP3 (short for Moving Pictures Experts Group, audio layer 3) allowed music from CDs to be condensed into song files small enough to be sent easily across the Internet.